fix(kubernetes): validate sandbox names against RFC 1123 requirements

[2000krysztof]

Summary

This PR adds a call to the validate_kubernetes_dns1123_label inside of create_sandbox function.

Related Issue

Fixes #2115

Changes

• display errors if the name is invalid
• calls the validation function inside of the create_sandbox function to intercept the name before the creation happens to display the error

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)
• This was also tested on an openshift 4.21 cluster to verify if the changes actually work

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[elezar]

Thanks for adding validation before the Kubernetes API call. I think this should reuse the DNS-1123 validation we already have instead of introducing a second sandbox-name validator.

crates/openshell-driver-kubernetes/src/driver.rs already defines validate_kubernetes_dns1123_label() and validate_kubernetes_dns1123_subdomain() near the existing driver volume validation code. The label helper enforces the same shape needed here: non-empty, max 63 chars, lowercase alphanumeric or -, and start/end alphanumeric. It is already covered by the driver-config DNS-1123 tests.

Please replace the new validate_k8s_name() implementation with a call like:

validate_kubernetes_dns1123_label(&sandbox.name, "sandbox.name")
    .map_err(KubernetesDriverError::InvalidArgument)?;

That keeps the Kubernetes driver on one validation primitive and avoids two slightly different RFC 1123 implementations drifting over time. If we want better sandbox-specific wording, we should add that around the existing helper or promote a shared helper into openshell_core, rather than duplicating the parsing logic.

[2000krysztof]

I have read the DCO document and I hereby sign the DCO.